1. Technical Field
Example embodiments of the present invention relate to a method and apparatus for cylinder pressure estimation in an engine management system for an internal combustion engine.
2. Related Art
An engine management system for an internal combustion engine controls many parameters of engine operation.
In order to achieve efficient low emission combustion, a modern engine management system controls fuel injectors to inject a target mass of fuel for each combustion. The fuel flow through an injector is a function of a pressure drop across the injector between a fuel supply line and the interior of the combustion chamber in which the combustion is to take place. The desired fuel mass is typically performed based on the pressure of the fuel in the supply line and width of a pulse controlling the time that the injector is open to release fuel into the combustion chamber.
To achieve the target fuel mass, the width of the injector pulse needs to be compensated for a pressure drop across the injector. For example, in a direct injection engine, the injector pressure drop corresponds to the fuel line, or fuel rail, pressure minus the pressure in the combustion chamber (for example, in the combustion chamber of the cylinder). However, during compression injection, the pressure drop across the injector varies because of changing cylinder pressure due to movement of the piston within the cylinder and the injection of the fuel.
Due to the adverse environment with a combustion chamber, it is not currently economically practical to accurately measure the pressure within the combustion chamber. Accordingly, an example embodiment of the invention seeks to provide an estimation of the pressure within the combustion chamber during at least part of a combustion cycle, to enable more accurate compensation for the differential pressure across the injector.